Arylarsonate- and Phosphonate-Capped Polyoxomolybdates, [(RC6H4As)2Mo6O24]n- and [(R'C6H4P)2Mo5O21]n.

We report on the synthesis and structural characterization of four arylarsonate- and phosphonate-capped polyoxomolybdates that exhibit different organic substituents in the para position of the phenyl group. The reaction of arylarsonates (RAsO3, wherein R = 4-BrC6H4 or 4-N3C6H4) with molybdate in aqueous pH 3.5 media resulted in the cyclic hexamolybdates [(BrC6H4As)2Mo6O24]4- (Mo6As2La) and [(N3C6H4As)2Mo6O24]4- (Mo6As2Lb), whereas the reaction of arylphosphonates (R'PO3, wherein R' = 4-O2CC6H4 or 4-O2CC6H4CH2) with molybdate in aqueous pH 3 media resulted in the cyclic pentamolybdates [(O2CC6H4P)2Mo5O21]6- (Mo5P2Lc) and [(HO2CC6H4CH2P)2Mo5O21]4- (Mo5P2Ld), respectively. Polyanions Mo6As2La and Mo6As2Lb comprise a ring of six MoO6 octahedra that is capped on either side by an organoarsonate group, whereas Mo5P2Lc and Mo5P2Ld consist of a ring of five MoO6 octahedra that is capped on either side by an organophosphonate group, with the organic arms protruding away from the metal-oxo core of the polyanions. All four polyanions Mo6As2La, Mo6As2Lb, Mo5P2Lc, and Mo5P2Ld have been characterized in the solid state by single-crystal X-ray diffraction, IR spectroscopy, and thermogravimetric and elemental analysis and in solution by multinuclear NMR (31P, 13C, and 1H). The synthetic procedure of (4-bromophenyl)arsonic acid, BrC6H4AsO3H2, is reported here for the first time.

Shape and Size Tuning of BiIII-Centered Polyoxopalladates: High Resolution 209Bi NMR and 205/206Bi Radiolabeling for Potential Pharmaceutical Applications.

We have discovered five bismuth(III)-containing polyoxopalladates (POPs) which were fully characterized by solution and solid-state physicochemical techniques: the cube-shaped [BiPd12O32(AsPh)8]5- (BiPd12AsL), [BiPd12O32(AsC6H4N3)8]5- (BiPd12AsLN), and [BiPd12O32(AsC6H4COO)8]13- (BiPd12AsLC) as well as the star-shaped [BiPd15O40(PO)10H6]11- (BiPd15P) and [BiPd15O40(PPh)10]7- (BiPd15PL), respectively. The organically modified capping groups phenylarsonate, p-azidophenylarsonate, and p-carboxyphenylarsonate were chosen as the azido (-N3) and carboxyl (-COOH) groups open up opportunities to covalently conjugate (via click reaction, amide coupling, etc.) with targeting vectors. The synthesis of p-azidophenylarsonate is reported here for the first time. The effects of the BiIII template and the organoarsonate vs -posphonate capping groups on the resulting POP shape (cube vs star) are discussed. The 209Bi NMR (I = 9/2) spectra of BiPd12AsL, BiPd12AsLN, and BiPd12AsLC revealed narrow peaks (ν1/2 ∼ 200 Hz) at 5470 ppm with a longitudinal relaxation time in the millisecond range (at 8.46 T). The absence of a quadrupolar relaxation contribution could be attributed to the allocation of BiIII in the highly symmetrical cuboid POP host cage. Similar peaks were absent in the 209Bi-NMR spectra of the star-shaped POPs BiPd15P and BiPd15PL due to the less symmetric coordination environment around the central BiIII ion. Further, 205/206Bi-radiolabeled POPs have been synthesized by incorporating a 205/206BiIII ion in the center of the POP structures. Carrier-free 205/206Bi radioisotopes (as surrogates of α-emitting 213Bi) were incorporated into the POP host-cage for the preparation of 205/206BiPd12AsL, 205/206BiPd12AsLN, 205/206BiPd12AsLC, and 205/206BiPd15PL, respectively. The radiometal incorporation was complete (>99% radiochemical yield) in 10 min according to radio-thin-layer chromatography. The 205/206BiPd12AsL polyanion was purified by solid-phase extraction. The incubation in rat serum showed the formation of a 205/206BiPd12AsL-protein aggregate.

A Mononuclear Co(II) Coordination Complex Locked in a Confined Space and Acting as an Electrochemical Water-Oxidation Catalyst: A "Ship-in-a-Bottle" Approach.

Preparing efficient and robust water oxidation catalyst (WOC) with inexpensive materials remains a crucial challenge in artificial photosynthesis and for renewable energy. Existing heterogeneous WOCs are mostly metal oxides/hydroxides immobilized on solid supports. Herein we report a newly synthesized and structurally characterized metal-organic hybrid compound [{Co3 (µ3 -OH)(BTB)2(dpe)2} {Co(H2O)4(DMF)2}0.5]n ⋅n H2O(Co-WOC-1) as an effective and stable water-oxidation electrocatalyst in an alkaline medium. In the crystal structure of Co-WOC-1, a mononuclear Co(II) complex {Co(H2O)4(DMF)2}(2+) is encapsulated in the void space of a 3D framework structure and this translationally rigid complex cation is responsible for a remarkable electrocatalytic WO activity, with a catalytic turnover frequency (TOF) of 0.05 s(-1) at an overpotential of 390 mV (vs. NHE) in 0.1 m KOH along with prolonged stability. This host-guest system can be described as a "ship-in-a-bottle", and is a new class of heterogeneous WOC.

Synthesis, characterization and magnetism of metal-organic compounds: role of the positions of the coordinating groups of a meso-flexible ligand in placing anisotropy to exhibit spin-canting behaviour.

In continuation of our recent investigation on flexible ligands, three new metal-organic coordination framework containing compounds, formulated as {Co(2)(L2)2(px3ampy)(2)}(n)·npx3ampy (1), {Co(L2)(px3ampy)(0.5)}(n) (2) and {Co(2)(L3) (px3ampy)(2)(H(2)O)}(n)·3nH(2)O (3) have been synthesized using three structurally different meso-flexible polycarboxylate ligands, H(2)L1(4,4'-methylenebis-(oxy)dibenzoic acid), H(2)L2 (3,3'-methylenebis-(oxy)dibenzoic acid) and H(4)L3 (5,5'-methylene-bis(oxy)diisophthalic acid) bearing the flexible spacer in the middle of the skeleton, along with a long flexible pyridyl ligand px3ampy (1,4-bis(3-pyridylaminomethyl)benzene). Compounds 1-3 have been characterized by single crystal X-ray diffraction analysis, IR spectroscopy and thermogravimetric (TG) studies including elemental analysis. The crystal structure determinations reveal that compound 1 has a 1D ladder-like structure and compounds 2and 3 are characterized by 3D frameworks. Compound 2 possesses a tiling of a snz net and compound 3 has a 3D interpenetrated motif with a (4,4) connecting 2-nodal net. The variable temperature magnetic susceptibility measurements demonstrate the dominating antiferromagnetic nature of all three title compounds; interestingly, however, compounds 2 and 3 exhibit ferromagnetic interactions due to the uncompensated magnetic moment of the system at low temperatures. Compound 2 illustrates the occurrence of spin canted antiferromagnetic ordering at T(c) ≈ 25 K with a coercive field (H(c)) of 900 Oe at 10 K due to the inclusion of magnetic anisotropy caused by the twisting of the concerned ligand skeleton. Compound shows comparatively weak ferromagnetic ordering with T(c) ≈ 9.5 K, for which weak magnetic anisotropy is present because of two different coordination environments (octahedral and tetrahedral) between two cobalt centers. A structure-function relationship has been described based on the position of the coordinating groups with respect to the flexible center of the ligand skeleton as well as the coordination angle between the ligand and the metal ion.